Plant parasitic nematodes inflict crop losses to world agriculture currently estimated to exceed $100 billion annually. Preventing this damage represents a significant challenge. With the impending loss of the fumigant methyl bromide, there is insufficient time to develop and register new synthetic compounds for nematode control.
Phytopathogenic nematodes are particularly difficult to control because they are covered with a thick, impermeable cuticle, or outer covering, and have very few sensory neurons. Since many pest control compounds operate as neurotoxins, the low number of neurons exposed by phytopathogenic nematodes decreases the effective target area for nematicidal compounds and has resulted in the development of nematicidal compounds with exquisitely high neurotoxic properties. Furthermore, because phytopathogenic nematodes are found in soil or plant roots, exposing the phytopathogenic nematodes to control agents is difficult to achieve and puts the water table at risk of contamination from those toxic compounds. The use of nematicides based on neurotoxins has been demonstrated to contaminate both ground and surface water. Consequently, many of these compounds are being removed from the market for public health reasons.
The reniform nematode, also known as Rotylenchulus reniformis, is the most economically important species in the genus Rotylenchulus. The females of reniform nematode cause extensive damage in the root system of plants by living partially inside roots. The term “reniform” refers to the kidney-shaped body of the mature females. Reniform can also cause the plants to be more susceptible to other disease-causing organisms.
Reniform nematodes parasitize the roots of a wide variety of plant species, including cotton, cowpea, sweet potato, soybean, pineapple, tea, and various vegetables such as tomato, okra, squash, and lettuce. Pathogenicity of reniform nematodes has greatly impacted agriculture. For example, they have caused a 40-60% reduction in cotton yield in Louisiana, along with an increase in Fusarium wilt.
Fumigation of soil prior to planting is a popular method for controlling nematodes. One of the most popular fumigants, methyl bromide, is slated for removal from use because of its ozone destroying properties. Furthermore, this practice of soil fumigation kills organisms in soil indiscriminately and runs the risk of eliminating beneficial microbes as well as disease organisms. The overall market for an effective nematicide with benign environmental effects is estimated to approach one billion dollars on a world-wide basis.
Pasteuria was first described in 1888 by Metchnikoff (Annales de l'Institut Pasteur 2:165-170) as a parasite of water fleas. Subsequently, Cobb described a Pasteuria infection of the nematode Dorylaimus bulbiferous (2nd ed. Hawaiian Sugar Planters Assoc., Expt. Sta. Div. Path. Physiol. Bull. 5:163-195, 1906).
The life cycle of the bacteria begins when endospores bind to the cuticle of the nematodes in soil. Pasteuria proliferate within the nematode body and pass through several documented morphological phases, including mycelial structures and thalli, culminating in the development of endospores. Endospores are released when the nematode body lyses. Growth of the bacteria within the nematode body reduces or eliminates the production of eggs by the nematode, severely restricting the rate of nematode reproduction. Economic damage to the host crop normally is inflicted by the first generation progeny of nematodes and is prevented by Pasteuria through lowering the concentration of progeny nematodes in the plant root zone.
While Pasteuria strains have been produced on multiple nematode species, such as Meloidogyne incognita (Verdeho, S. and R. Mankau. 1986. Journal of Nematology, 18:635) and Meliodogyne arenaria (U.S. Pat. No. 6,919,197), no Pasteuria strain has been observed or successfully cultivated on Reniform nematodes prior to now.